Extruded catheters and other flexible plastic tubing may, in many circumstances, require a greater degree of torsional or rotational stiffness than is normally provided by a conventional plastic material from which a catheter or tube may be extruded, such as polyethylene, polyvinyl chloride, polyurethane, or polyethylene terephthalate. For example, intravascular catheters for heart catheterization or PTCA need to be guided through the branching network of the patient's arterial system. Typically, such catheters may be "steered", in which the physician rotates the catheter, which may have a bent tip, to select a path when a blood vessel junction is encountered. For such a catheter, it is highly desirable to exhibit good rotational stiffness in addition to axial stiffness.
To provide such rotational stiffness, plastic catheters have been manufactured in the prior art with a tubular, braided wire sheath with is typically sealed within the catheter to provide added strength and rotational stiffness, as shown in Stevens U.S. Pat. No. 3,485,234, and 3,585,707, for example. Additionally, as shown in the pending application of Jeffery G. Gold et al., Ser. No. 270,810, filed Nov. 14, 1988 and entitled Catheter Having Sections Of Variable Torsion Characteristics, now U.S. Pat. No. 5,037,404 a tubular wire sheath is provided in which the angular relation of the wire strands vary along the length of the catheter, so that different sections of the catheter exhibit differing physical characteristics, particularly differing rotational stiffness.
There is a need to reduce the outer diameter of catheters by reducing their wall thickness, particularly those which are used in angiographic procedures, as well as other intravenous catheters. Catheters with reduced wall thickness penetrate smaller blood vessels with less trauma to blood vessel walls. The braided metal wire support which is typically carried in many such catheters clearly imposes a significant limitation on efforts to reduce the wall thickness. Accordingly, there is a significant need for a way to eliminate the metal support means in a catheter, while at the same time maintaining the necessary rotational and axial stiffness which is a major reason for the presence of such metal support means. If this can be accomplished, then the catheter outer diameter can be reduced to a dimension which is not possible when a metal support means is present, without reducing the lumen diameter, so that such catheters can penetrate more easily and more deeply into small arteries and the like without trauma to the artery wall.
By this invention, catheters and other tubing may be provided which do exhibit improved rotational stiffness by themselves, without the support provided by a braided wire sleeve or the like. Additionally, such catheters may be inherently stiffer in the longitudinal (axial) direction as well if desired, but to a degree which is relatively unrelated to the rotational stiffness, and which may be varied with respect to the rotational stiffness. Furthermore, improvements in strength of the catheter may also be provided. Also, the physical properties of the catheter of this invention may vary along the length thereof in a predetermined manner as may be deemed beneficial for the utility thereof.